Cilia are cellular organelles that are important for human development, organ function, and sensation. Defects in cilia formation or function results in devastating human diseases or ciliopathies, including autosomal dominant polycystic kidney disease (ADPKD). ADPKD affects 1/400-1000 individuals, often resulting in end- stage renal disease. In humans, mutations in the polycystin-1 or polycystin-2 receptor-channel complex cause ADPKD. Despite the profound medical importance of cilia in human health, how cilia are specialized in form and function remains poorly understood. This proposed research is focused on uncovering fundamental principals of cilia biology not possible in human studies or easily studied in vertebrate model systems. C. elegans is a transparent, multicellular animal with specialized sensory cilia, features that enable in vivo imaging that is unprecedented in its simplicity and reproducibility. We have developed the tools and reagents to study polycystin localization and function in C. elegans. We will employ genetic, molecular, imaging, biochemical, and electrophysiological approaches to address three specific aims. First, we will dissect polycystin signaling pathways. Next, we will determine the molecular details of mechanisms regulating polycystin localization, focusing on the roles of phosphoinositides and tubulin post-translational modifications. Finally, we will identify new genes regulating PKD-2 localization using transgenic animals that are hypersensitive to neuronal RNAi. This multidisciplinary approach will provide a comprehensive picture of the molecules that influence polycystin channel assembly and trafficking, and will provide critical insight to ciliary receptor trafficking in general. Thus these studies will have important implications in human diseases such as ADPKD in which cilia play an important and central role.